Trigeminal evoked potentials (TEP) were recorded by electrical stimulation of the lips in 7 patients with symptomatic trigeminal neuralgia due to CT proved mass lesions involving the trigeminal nerve. All the patients showed TEP abnormalities on the affected side. Chronic compression and irritation of the trigeminal nerve may be responsible for these changes. The results obtained were compared with other similar studies and TEP abnormalities observed in idiopathic trigeminal neuralgia. As all the patients had unequivocal compression of the trigeminal nerve and all of them had TEP changes, it can be concluded that TEP abnormality is an accurate predictor of trigeminal nerve compression. TEPs may be a valuable aid in demonstrating a compressive element in patients with trigeminal neuralgia.